ARLINGTON — The A’s have just 13 games left in the regular season, a potential wild card berth hangs between each one. But the ups, downs and uncertainty don’t faze this team much; many key players are just pacing even-keeled at extraordinary rates.

Here are three key statistics to keep an eye on as the regular season winds down.

Marcus Semien’s 113 runs.

Even though it determines who wins and loses a game, runs is a somewhat antiquated stat. Generally, it does little to contextualize an individual player’s isolated impact.

That isn’t necessarily the case for Semien, who ranks tied for third in the American League in runs…as a leadoff hitter. It speaks to his consistency over the season — he’s played all 149 games this season with a 229-game streak overall.

Close attention to the intricacy of an at-bat brought Semien to the next level as a hitter. But just the sheer volume of at-bats at a production level that barely wavers has made Semien a premier leadoff batter. He’s always on base, so he’s always sprinting home (plus, he’s batting .333 with runners in scoring position). Semien’s 6.5 WAR — which includes defense — ranks seventh in baseball, but, if anything a somewhat antiquated stat like runs tells us more about Seimen’s irreplaceable presence on the team this year.

Sean Manaea’s 0.75 ERA

Small sample size, of course. Manaea’s ERA doesn’t mean much in baseball’s grand scheme, but it tells us about his mettle upon returning to the big leagues after nearly a year absence following arthroscopic shoulder surgery.

Manaea has two 2019 starts so far, but this trajectory has him as the most probable candidate to start a wild card game. He may not last beyond the fifth inning, but that may be all the team needs from him (say, if Jesús Luzardo can come out of the bullpen for a few innings?).

His fastball topped out at 94 mph against Aaron Judge at Yankee Stadium, but has mostly hovered around the high-80s and low-90s. But Manaea’s sling-shot arm angle creates the type of deception that generate big swings and misses. He’s clearly fooling hitters.

In his 2019 debut in New York, Manaea struck out five in five shutout innings. Running out of steam toward the end of his outing, he walked three batters in the sixth. Against the Detroit Tigers, Manaea struck out 10 in seven shutout innings and gave up one home run. It’s clear that Manaea not only has swing-and-miss stuff without the velocity, but has quickly returned to his post as one of the A’s more reliable starters (and it’s a crowded group to join at the moment).

With Chris Herrmann’s release, September call-up Sean Murphy is the No. 2 catcher who really quickly has most-likely become the No. 1 catcher as the regular season transitions into the postseason.

He makes a clear impact defensively; he has quick feet and is a great framer. But he’s also knocking the snot out of the ball. He averages a 94 mph exit velocity, but (maybe obviously) is particularly powerful on his balls in play. His four home runs came off the bat at 100, 105, 110 and 106 mph, respectively. Two of his three doubles had 111 and 108 mph exit velocities (the third at 55 mph, he can do it all!).

Murphy isn’t technically eligible for the postseason (since he wasn’t on the 40-man as of August 31), but the A’s can and will petition the Commissioner to get him on that roster. He’s clearly unafraid of the moment with not just great chemistry with the pitching staff, but power that can’t be ignored.